Devices are known in the art in which braking pressure is generated by a counterbalance valve of a return side pipe of a motor for traveling and oil within a circuit that is heated to a high temperature as a result of the occurrence of the braking pressure is discharged to a tank via an overload relief valve so as to suppress increases in oil temperature within the conduit line (see Patent Reference 1). With the device disclosed in Patent Reference 1, when an accelerator pedal is not being operated during traveling and a control valve returns to a neutral position, the circuit is replenished with oil from a tank via a check valve and the occurrence of cavitation is prevented.
Patent Reference 1: Japanese Patent Publication Laid-open No. 2003-254305